Shcherbatenko, M., Lobanov, Y., Benderov, O., Shurakov, A., Ignatov, A., Titova, N., et al. (2015). Antenna-coupled 30 THz hot electron bolometer mixers. In Proc. 26th Int. Symp. Space Terahertz Technol. (27).
Abstract: We report on design and characterization of a superconducting Hot Electron Bolometer Mixer integrated with a logarithmic spiral antenna for mid-IR range observations. The antenna parameters have been adjusted to achieve the ultimate performance at 10 µm (30 THz) range where O3, NH3, CO2, CH4, N2O,…. lines in the Earth’s atmosphere, in planetary atmospheres and in the interstellar space can be observed. The HEB mixer is made of a thin NbN film deposited onto a GaAs substrate. To couple the radiation we rely on the quasioptical approach: the device is glued to a semi-spherical germanium lens with diameter~ 3 mm. A wet cryostat equipped with a germanium window and narrow band-pass filter is used to characterize the antenna and estimate the mixer performance.
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Cherednichenko, S., Yagoubov, P., Il'in, K., Gol'tsman, G., & Gershenzon, E. (1997). Large bandwidth of NbN phonon-cooled hot-electron bolometer mixers. In Proc. 27th Eur. Microwave Conf. (Vol. 2, pp. 972–977). IEEE.
Abstract: The bandwidth of NbN phonon-cooled hot electron bolometer mixers has been systematically investigated with respect to the film thickness and film quality variation. The films, 2.5 to 10 nm thick, were fabricated on sapphire substrates using DC reactive magnetron sputtering. All devices consisted of several parallel strips, each 1 um wide and 2 um long, placed between Ti-Au contact pads. To measure the gain bandwidth we used two identical BWOs operating in the 120-140 GHz frequency range, one functioning as a local oscillator and the other as a signal source. The majority of the measurements were made at an ambient temperature of 4.2 K with optimal LO and DC bias. The maximum 3 dB bandwidth (about 4 GHz) was achieved for the devices made of films which were 2.5-3.5 nm thick, had a high critical temperature, and high critical current density. A theoretical analysis of bandwidth for these mixers based on the two-temperature model gives a good description of the experimental results if one assumes that the electron temperature is equal to the critical temperature.
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Lobanov, Y., Tong, C., Blundell, R., & Gol'tsman, G. (2009). A study of direct detection effect on the linearity of hot electron bolometer mixers. In Proc. 20th Int. Symp. Space Terahertz Technol. (pp. 282–287).
Abstract: We have performed a study of how direct detection affects the linearity and hence the calibration of an HEB mixer. Two types of waveguide HEB devices have been used: a 0.8 THz HEB mixer and a 1.0 THz HEB mixer which is ~5 times smaller than the former. Two independent experimental approaches were used. In the ΔG/G method, the conversion gain of the HEB mixer is first measured as a function of the bias current for a number of bias voltages. At each bias setting, we carefully measure the change in the operating current when the input loads are switched. From the measured data, we can derive the expected difference in gain between the hot and cold loads. In the second method (injection method [1]), the linearity of the HEB mixer is independently measured by injecting a modulated signal for different input load temperatures. The results of both approaches confirm that there is gain compression in the operation of HEB mixers. Based on the results of our measurements, we discuss the impact of direct detection effects on the operation of HEB mixers.
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Shurakov, A., Tong, E., Blundell, R., & Gol'tsman, G. (2012). Microwave stabilization of HEB mixer by a microchip controller. In IEEE MTT-S international microwave symposium digest (pp. 1–3).
Abstract: The stability of a Hot Electron Bolometer (HEB) mixer can be improved by the use of microwave injection. In this article we report a refinement of this approach. We introduce a microchip controller to facilitate the implementation of the stabilization scheme, and demonstrate that the feedback loop effectively suppresses drifts in the HEB bias current, leading to an improvement in the receiver stability. The measured Allan time of the mixer's IF output power is increased to > 10 s.
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Lobanov, Y. V., Tong, C. - Y. E., Hedden, A. S., Blundell, R., & Gol'tsman, G. N. (2010). Microwave-assisted슠measurement슠of the슠frequency슠response슠of슠terahertz슠HEB슠mixers슠with a슠fourier슠transform슠spectrometer. In 21st International Symposium on Space Terahertz Technology (pp. 420–423).
Abstract: We describe a novel method of operation of the HEB direct detector for use with a Fourier Transform Spectrometer. Instead of elevating the bath temperature, we have measured the RF response of waveguide HEB mixers by applying microwave radiation to select appropriate bias conditions. In our experiment, a microwave signal is injected into the HEB mixer via its IF port. By choosing an appropriate injection level, the device can be operated close to the desired operating point. Furthermore, we have shown that both thermal biasing and microwave injection can reproduce the same spectral response of the HEB mixer. However, with the use of microwave injection, there is no need to wait for the mixer to reach thermal equilibrium, so characterisation can be done in less time. Also, the liquid helium consumption for our wet cryostat is also reduced. We have demonstrated that the signalto-noise ratio of the FTS measurements can be improved with microwave injection.
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Shurakov, A., Maslennikov, S., Tong, C. -yu E., & Gol’tsman, G. (2015). Performance of an HEB direct detector utilizing a microwave reflection readout scheme. In Proc. 26th Int. Symp. Space Terahertz Technol. (36).
Abstract: We report the results of our study on the performance of a hot electron bolometric (HEB) direct detector, operated by a microwave pump. The HEB devices used in this work were made from NbN thin film deposited on high resistivity silicon with an in-situ fabrication process. The experimental setup employed is similar to the one described in [1]. The detector chips were glued to a silicon lens clamped to a copper holder mounted on the cold plate of a liquid helium cryostat. Thermal link between the lens and the holder was maintained by a thin indium shim. The HEBs were operated at a bath temperature of about 4.4 K. Conventional phonon pump, commonly realized by raising the bath temperature of the detector, was substituted by a microwave one. In this case, a CW microwave signal is injected to the device through a directional coupler connected directly to the detector holder. The power incident on the HEB device was typically 1-2 μW, and the pump frequency was in the range of 0.5-1.5 GHz. The signal sources were 2 black bodies held at temperatures of 295 K and 77 K. A chopper wheel placed in front of the cryostat window switched the input to the detector between the 2 sources. A modulation frequency of several kilohertz was chosen in order to reduce the effects of the HEB’s flicker noise. A cold mesh filter was used to define the input bandwidth of the detector. The reflected microwave signal from the HEB device was fed into a low noise amplifier, the output of which is connected to a room temperature Schottky microwave power detector. This Schottky detector, in conjunction with a lock-in amplifier, demodulated the input signal modulation from the copper wheel. As the input load was switched, the impedance of the HEB device at the microwave pump frequency also changed in response to the incident signal power variation. Therefore the reflected microwave power follows the incident signal modulation. The derived responsivity from this detection system nicely correlates with the HEB impedance. In order to provide a quantitative description of the impedance variation of the HEB device and the impact of a microwave pump, we have numerically solved the heat balance equations written for the NbN bridge and its surrounding thermal heat sink [2]. Our model also accounts for the impact of the operating frequency of the detector because of non-uniform absorption of low-frequency photons across the NbN bridge [3]. In our measurements we varied the signal source wavelength from 2 mm down to near infrared range, and hence we indirectly performed the impedance measurements at frequencies below, around and far beyond the superconducting gap. Preliminary results show good agreement between the experiment and theoretical prediction. Further measurements are still in progress. [1] A. Shurakov et al., “A Microwave Reflection Readout Scheme for Hot Electron Bolometric Direct Detector”, to appear in IEEE Trans. THz Sci. Tech., 2015. [2] S. Maslennikov, “RF heating efficiency of the terahertz superconducting hot-electron bolometer”, http://arxiv.org/pdf/1404.5276v5.pdf, 2014. [3] W. Miao et al., “Non-uniform absorption of terahertz radiation on superconducting hot electron bolometer microbridges”, Appl. Phys. Let., 104, 052605, 2014.
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Ozhegov, R. V., Smirnov, A. V., Vakhtomin, Y. B., Smirnov, K. V., Divochiy, A. V., & Goltsman, G. N. (2009). Ultrafast superconducting bolometer receivers for terahertz applications. In Proc. PIERS (867). 777 Concord Avenue, Suite 207 Cambridge, MA 02138: The Electromagnetics Academy.
Abstract: The research by the group of Moscow State Pedagogical University into the hot-electron phenomena in thin superconducting films has led to the development of new types of detectors and their use both in fundamental and applied studies. In this paper, we present the results of testing the terahertz HEB receiver systems based on ultrathin (∼ 4 nm) NbN and MoRe detectors with a response time of 50 ps and 1 ns, respectively. We have developed three types of devices which differ in the way a terahertz signal is coupled to the detector and cover the following ranges: 0.3–3 THz, 0.1–30 THz and 25–70 THz. In the case of the receiving system optimized for 0.3–3 THz, the sensitive element (a strip of asuperconductor with planar dimensions of 0.2μm (length) by 1.7μm (width)) was integrated witha planar broadband log-spiral antenna. For additional focusing ofthe incident radiation a silicon hyperhemispherical lens was used. For the 0.1–30 THz receivingsystem, the sensitive element was patterned as parallel strips(2μm wide each) filling an area of 500×500μm2with a filling factor of 0.5. In the receivingsystem of this type we used direct coupling of the incident radiation to the sensitive element. Inthe 25–70 THz range (detector type 2/2a in Table 1) we used a square-shaped superconductingdetector with planar dimensions of 10×10μm2. Incident radiation was coupled to the detectorwith the use of a germanium hyperhemispherical lens.The response time of the above receiving systems is determined by the cooling rate of the hotelectrons in the film. That depends on the electron-phonon interaction time, which is less forultrathin NbN than in MoRe.
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Zhang, W., Miao, W., Zhong, J. Q., Shi, S. C., Hayton, D. J., Vercruyssen, N., et al. (2013). Temperature dependence of superconducting hot electron bolometers. In Not published results: 24th international symposium on space terahertz technology.
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Gol'tsman, G. N., Elant'iev, A. I., Karasik, B. S., & Gershenzon, E. M. (1993). Antenna – coupled superconducting electron-heating bolometer. In Proc. 4th Int. Symp. Space Terahertz Technol. (pp. 623–628).
Abstract: We propose a novel antenna-coupled superconducting bolometer based on electron-heating in the resistive state. A short narrow ultrathin super- conducting film strip (sized approximately 4x1x0.01 pm 3 ), which is in good thermal contact with the thermostat, serves as a resistive load for infrared or submillimeter current. In contrast to conventional isothermal super- conducting bolometers electron-heating ones can have a higher sensitivity which grows when filni. thickness is reduced. Response time of electron- heating bolometer does not depend on heat transfer from the film to the enviroment. To calculate the sensitivity (NEP), we have used experimental data on wideband Al, Nb and NbN bolometers which have the same un- derlying physical mechanism. The bolom.eters have been made in the form of a structure composed of a number of long narrow strips. The values of for Al, NEP have been found to be 1.5 . 113 -16 1 140 -15 ) and 2 . 10 – 14werT,-1/2 – Nb and NbN respectively. In the paper, the prospects are also discussed of improving the picosecond YBaCuO detector, developed recently. NEP value of the detector, if combined with a microantenna, can reach the order of 10- •ilz-v2.
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Elmanov, I., Sardi, F., Xia, K., Kornher, T., Kovalyuk, V., Prokhodtsov, A., et al. (2020). Development of focusing grating couplers for lithium niobate on insulator platform. In J. Phys.: Conf. Ser. (Vol. 1695, 012127).
Abstract: In this paper, we fabricate and experimentally study focusing grating couplers for lithium niobate on an insulator photonic platform. The transmittance of a waveguide equipped with in- and out-couplers with respect to the grating period is measured with and without silicon dioxide cladding applied. Our results show the influence of silicon dioxide cladding on the efficiency and the central wavelength of grating couplers and can be used to improve grating coupling efficiency. Our study is supported by numerical simulations.
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